Shaped contoured crushable structural members and methods for making the same

ABSTRACT

Shaped, contoured crushable structural members and methods for making the same are described. The contoured structural members comprise composite or metal materials sandwiching a support or stabilizing structure. The structural members are made crushable by incorporating an initiator into the structural members. The structural member crushes at the location of the initiator by absorbing the energy of an exerting load. The shaped structure is provided by bending the generally straight shape of the structural member. With a shaped, contoured, crushable, and generally non-flat structure, applications and uses for the structural members of the present invention are nearly limitless.

REFERENCES TO RELATED APPLICATIONS

This application claims priority from U.S. provisional patent application No. 60/216,636, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to structural members and methods for making the same. In particular, the present invention relates to shaped, contoured crushable composite parts and methods for making the same.

BACKGROUND OF THE INVENTION

In recent years there has been an increasing emphasis on the use of lightweight composite materials. One application, for example, has been their use to improve the efficiency of motor vehicles. To that end, the United States Government and the U.S. Council for Automotive Research (USCAR)—which represents Daimler Chrysler, Ford, and General Motors have partnered to form the Partnership for a New Generation of Vehicles (PNGV). One goal of PNGV is to develop technology, such as composite technology, that can be used to create environmentally friendly vehicles with up to triple the fuel efficiency, while providing today's affordability, performance and safety. For example, PNGV wants to improve the fuel efficiency of today's vehicles from about 28 miles per gallon (mpg) to about 83 mpg and a 40-60% decrease in the present curb weight (3200 pounds).

One method to improve the fuel efficiency is to decrease the weight of today's vehicles and use lighter weight materials. The materials used in today's vehicles, such as steel and aluminum, are quite heavy relative to composite materials, but have been necessary to provide sufficient structural properties, including tensile, compression, flexural, interlaminar shear, and in-plane shear strengths and other mechanical and material properties, to meet vehicle design requirements.

Many other applications of lightweight composites have been made to supplement or replace the use of structural materials, such as steel, cast iron, and aluminum. These include buildings, bridges, recreational vehicles, aerospace, defense, and sporting goods, as well as many other applications.

One way to increase the structural properties of materials, particularly the torsional or flexural strength, is to make them in a more structurally efficient form. In one structurally efficient form, metals like aluminum and steel have been combined with a supporting structure, such as a honeycomb core material, by sandwiching the honeycomb between panels of the metal. Examples of such combinations have been described in U.S. Pat. Nos. 4,291,205, 5,140,913, 5,192,623, 5,635,306, 5,875,596, and 5,899,037, the disclosures of which are incorporated herein by reference. In another structurally efficient form, composite materials have been combined with a supporting structure, such as a honeycomb or foam structure, by sandwiching the supporting structure between panels of the composite material. Examples of such combinations have been described in U.S. Pat. Nos. 5,006,391, 5,195,779, 5,652,039, 5,834,082, 5,848,767, 5,849,122, and 5,875,609, the disclosures of which are incorporated herein by reference.

Such combinations, however, have been generally limited to relatively flat structures and so applications of such materials have been quite limited. As well, the structural members have not been able to be shaped or bent into various complex shapes, including substantially non-straight shapes, necessary to enhance their end-use.

SUMMARY OF THE INVENTION

The present invention provides shaped contoured crushable structural members and methods for making the same. The contoured structural members comprise composite or metal materials sandwiching a support or stabilizing structure. The structural members are made crushable by incorporating an initiator into the structural members. The structural member crushes at the location of the initiator by absorbing the energy of an exerting load. The shaped structure is provided by bending the generally straight shape of the structural member. With a shaped, contoured, crushable, and generally non-flat structure, applications and uses for the structural members of the present invention are nearly limitless.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-20, 20A, 21, 21A, and 22-24 are views of structural members and methods of making the same according to the invention. FIGS. 1-20, 20A, 21, 21A, and 22-24 presented in conjunction with this description are views of only particular—rather than complete—portions of the structural members and methods of making the same according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description provides specific details in order to provide a thorough understanding of the present invention. The skilled artisan, however, would understand that the present invention can be practiced without employing these specific details. Indeed, the present invention can be practiced by modifying the illustrated structural member and method and can be used in conjunction with apparatus and techniques conventionally used in the industry.

FIG. 1 illustrates one contoured structural member—a tubular member with a substantially circular cross-section—according to the present invention. In the context of the present invention, a “contoured” structural member is any shape, size, or configuration where at least one portion of the outer or inner periphery of such member is substantially non-flat, including curved, geometric or irregular. Preferably, the contoured structural members have a closed surface configuration, such as a surface facilitating their manufacture as explained below. In the context of the present invention, a “closed” structural member is one having any shape, size, or configuration where at least one portion of the surface (inner and/or outer) of such member is a substantially closed or substantially continuous. Examples of a closed configuration include a tubular, substantially spherical, polygonal, conical, or other similar shape, as well as those illustrated and described herein. In one aspect of the invention, a contoured structural member is one that has a wall that completely or substantially circumscribes an interior space, regardless of the circumferential or peripheral shape of the member.

The structural members of the present invention may have a cylindrical or a non-cylindrical configuration such as cones, pyramid, pods, hemispheres or spheres. The structural members of the present invention may also have a circular or a non-circular cross-section such as rectangular, square, hexagonal, octagonal, or the like. They may also comprise very irregular, non-closed, substantially planar surfaces. Indeed, the structural members of the present invention could have any complex contoured shape or combination of contoured shapes as described in detail below. The structural members of the present invention are characterized by the fact that they are substantially non-flat and thereby distinguished from known sheet-shaped cored composite structures.

In FIG. 1, tubular structural member 2 comprises inner section or portion 4, optional intermediate section or portion 6, outer section or portion 8, and optional core region 10. Inner portion 4, outer portion 8, and optional core region 10, can be made of any suitable composite material as described below. Optional intermediate portion 6 is a “cored” structure that attaches to and supports and/or stabilizes the inner and outer portions.

Core region 10 is located in an inner section of structural member 2 and, as described below, is about the size of the substrate or mandrel used in forming the structural member. Core region 10 can be of any suitable size, shape, or configuration depending primarily on the removable mandrel(s) in the manufacturing process used to make structural member 2, the configuration of structural member 2, and the desired end application of structural member 2.

Core region 10 may be hollow, but may optionally be partially or completely filled with any desired core material such as foam, plastic, conducting or insulating materials, metals, and/or the like. Core region 10 containing the core material may be a structural element. The core material may also be added after structural member 2 is formed, or formed integrally into the structure. If the core material is added after the formation of structural member 2, it may be attached to structural member 2 using an adhesive or other suitable bonding means known in the art.

The materials for inner section 4 and outer section 8 can be the same or different materials. Preferably, inner portion 4 and outer portion 8 comprise the same material. In one aspect of the invention, the materials for the inner or outer portions comprise any suitable reinforced resin matrix material (RRMM), which is a resin matrix material (RMM) with continuous or discontinuous reinforcement material embedded in the resin matrix. In one aspect of the invention, the RMM is a organic resin matrix material (ORMM). See, for example, U.S. Pat. Nos. 5,725,920 and 5,309,620, the disclosures of which are incorporated herein by reference.

In one aspect of the invention, the ORMM can be a thermoset resin. Thermoset resins are polymeric materials which set irreversibly when heated. Examples of thermoset resins include epoxy, bismeleimide, polyester, phenolic, polyimide, melamine, xylene, urethane, phenolic, furan, silicone, vinyl ester, and alkyd resins, or combinations thereof. The thermoset resins can contain various additives as known in the art, such as cross-linking agents, curing agents, fillers, binders, or ultraviolet inhibitors. Preferably, epoxy, vinyl ester, or polyester resins are employed as the thermoset resin in the present invention

In another aspect of the invention, the ORMM can be a thermoplastic resin matrix material. Thermoplastic resins are polymeric materials which do not set irreversibly when heated, e.g., they soften when exposed to heat and then return to their original condition when cooled. Examples of thermoplastic resins include polypropylene, polyethelene, polyamides (nylons), polyesters (PET, PBT), polyether ketone (PEK), polyether ether ketone(PEEK), polyphenylene sulfide (PPS), polyphenylene oxide (PPO) and its alloys, and polyvinyl resins, or combinations thereof. The thermoplastic resins can contain various additives as known in the art, such as cross-linking agents, curing agents, fillers, binders, or ultraviolet inhibitors. Preferably, polyamides (nylons), polyester, polycarbonate and polypropylene resins are employed as the thermoplastic resin in the present invention.

The material used to reinforce the RMM of the present invention can be in any form which reinforces the resin matrix. Examples of reinforcement forms include unidirectional tape, multidirectional tapes, woven fabrics, roving fabrics, matt fabrics, preforms, fibers, filaments, whiskers, and combinations thereof. The type of material used to reinforce the RMM can be any type serving such a reinforcing function. Preferably, the form of the reinforcement materials for the resin matrix is a fiberous material, such as continuous or discontinuous fibers. Examples of materials that can be employed in the present invention include glass-s, glass-e, aramid, graphite, carbon, ultra-high molecular weight polyethylene, boron, silicon carbide, ceramic, quartz, metals, isotropic metals (aluminum, magnesium and titanium), metal coated organic fibers, CAMP, hybrids of these fibers, or combinations of these fibers. See, for example, U.S. Pat. No. 6,117,534, the disclosure of which is incorporated herein by reference.

In yet another aspect of the invention, non- or partially-cured composite materials are used as the material for the inner and/or outer sections. Composites are a mixture or combination, on a macro scale, of two or more materials that are solid in the finished state, are mutually insoluble, and differ in chemical nature. Any composites known in the art such as laminar, particle, fiber, flake, and filled composites can be employed in the invention. The non- or partially-cured composite materials are a ORMM (thermoset or thermoplastic resin) reinforced with a continuous fiber.

Preferable composite materials used for inner section 4 and outer section 8 include B-stage prepreg materials typically in the form of sheets or laminates, which can be formed by impregnating a plurality of fiber reinforcement tows with a formulated resin. Methods of making B-stage prepreg sheets and the sheets themselves are well known. See, for example, those sheets described in U.S. Pat. No. 4,495,017, the disclosure of which is incorporated herein by reference. When cured, prepreg materials are generally stronger and stiffer than metals while providing greater resistance to fatigue, chemicals, wear and corrosion. Preferable reinforcement for prepregs include aramids, glass materials, nickel carbide, silicone carbide, ceramic, carbons and ultra-high molecular weight polyethylene, or a combination thereof. See, for example, U.S. Pat. Nos. 4,968,545, 5,102,723, 5,499,661, 5,579,609, and 5,725,920, the disclosures of which are incorporated herein by reference. Carbon, glass, metals and especially isotropic metals like aluminum, magnesium and titanium, metal-coated organic fibers, and aramid fibers, or a combination thereof, can also be employed as the fibers. See, for example, U.S. Pat. Nos. 5,601,892 and 5,624,115, the disclosures of which are incorporated herein by reference. Preferably, carbon fibers, glass fibers, or -aramid fibers and more preferably Kevlar 29 or 49 fibers are employed in the present invention.

The fiber volume in the prepregs may be varied so as to maximize the mechanical, electrical, and thermal properties. See, for example, U.S. Pat. No. 5,848,767, the disclosure of which is incorporated herein by reference. High fiber volume parts are stiffer and, in the case of thermally conductive fibers, the parts are more thermally conductive. Fiber volumes in the present invention can range from about 5% to about 95%, and preferably range from about 50% to about 65%. The fibers of the prepregs may be oriented within the prepreg material in any desired direction as known in the art, such as about 0 to about 90 degrees, including equal numbers of fibers balanced in opposing directions. See, for example, U.S. Pat. No. 4,946,721, the disclosure of which is incorporated herein by reference.

In yet another aspect of the invention, sheet molding compounds (SMCs) can be used as the materials for the inner or outer portion. SMCs are sheets made up of B-stage thermoset resin reinforced with a discontinuous fiber. SMCs are fully formulated ORMM compounds having discontinuous fiber reinforcement materials which are typically formed into sheet, ply, or laminate-without additional preparation. See, for example, U.S. Pat. No. 6,103,032, the disclosure of which is incorporated herein by reference. The resins that can be used in the SMCs of the present invention include any of the thermoset resins listed above. Preferably, polyester, vinyl esters, or epoxy resins are employed as the resin in SMCs of the present invention. The fibers that can be used in the SMCs of the present invention include any of those listed above. Preferably, glass, carbon, or aramid fibers-, and more preferably Kevlar 29 or 49 fibers can be used as the fibers in the SMCs. The fiber volume in the SMC may also be varied so as to maximize the mechanical and thermal properties.

With an unsaturated resin system as its base, SMCs incorporate other materials for desirable processing and molding characteristics and optimum physical and mechanical properties, such as mechanical strength, impact resistance, stiffness, and dimensional stability. These incorporated materials include polymers, fibers for reinforcement, resins, fillers, initiators to promote polymerization, viscosity agents, lubricants, mold release agents, catalysts, thickeners, pigments, polyethylene powders, flame retardants, ultraviolet absorbing agents, and other additives. Each of the additives can provide important properties to the SMC, either during the processing or molding steps or in the finished parts, and can be incorporated in the SMCs of the present invention.

In one aspect of the invention, inner section 4 and outer section 8 contain at least one layer of such ORMM materials. One layer is sufficient to form the respective inner or outer section and provide the desired structural characteristics for structural member 2. Additional layers can be added to improve the strength, stiffness, or other physical characteristics of structural member 2. It is possible to use a single layer with fibers having complementary orientations. It is preferred, however, to use a plurality of layers with complementary orientations to balance intrinsic stresses in the layers that make up the sections that result when, as described below, the B-stage materials are fully cured. To be complementary, the fibers in successive layers should be symmetric and balanced (e.g., by having the fibers offset from the sheet axis by equal and opposite amounts from one layer to another) as shown in FIG. 2. The fibers can also be oriented to meet the design parameters of the component into which they are being incorporated, e.g., to optimize the structural strength against the expected load. The fibers could be oriented at any suitable angle, including at angles ranging from 0 to about 90 degrees, including in ±15, ±30, ±45, ±60, and ±75 degrees, or as otherwise known in the art. See, for example, U.S. Pat. Nos. Re. 35,081 and 5,061,583, the disclosures of which are incorporated herein by reference.

In yet another aspect of the invention, the materials for the inner or outer portions can comprise any suitable metal-containing materials, such as a light or heavy metal or alloys thereof. Suitable light metals include magnesium, aluminum, titanium, zinc, molybdenum, or alloys thereof. Suitable heavy metals include iron, copper, nickel, carbon steel, stainless steel, alloy steel, tin, or alloys thereof.

Since metal-containing materials comprise isotropic fibers, which exhibit similar strength characteristics in all directions, one layer of the metal-containing material is sufficient to form the respective inner or outer portion and provide the desired structural characteristics. Additional layers of the metal-containing material, depending on cost and structural considerations, can also be used to give the desired thickness of the inner or outer portion. Indeed, successive layers of different metal-containing materials may be employed as the inner and/or outer portion.

The configuration of inner portion 4, optional intermediate portion 6, and outer portion 8 can vary within structural member 2. For example, the materials used for the composite, the fiber orientation, and the curvature, thickness, shape and other characteristics of the inner and/or outer portions (4, 8) can differ along the length and width of structural member 2. See, for example, U.S. Pat. No. 5,718,212, the disclosure of which is incorporated by reference.

Optional intermediate portion 6 of the structural member 2 of the present invention has any structure which spaces and/or supports inner portion 4 and outer portion 8, as well as enhances the structural properties of those two portions when placed there between. Further, intermediate section 6 can be made of any suitable material which separates, supports, stabilizes, couples and attaches inner portion 4 with respect to outer portion 8. Interposing intermediate section 6 between inner section 4 and outer section 8 improves the structural properties according to well-known principles of engineering mechanics and mechanical engineering of structural member 2 over the properties of a member comprising only appropriately shaped inner section 4 and outer section 8 bonded together. Preferably, as illustrated in FIG. 1, the intermediate portion is substantially contiguous with the outer surface of inner section 4 and the inner surface of outer section 8, e.g., the intermediate section 6 contacts the inner section 4 and/or the outer section 8 at discrete points over most—if not all—of their surfaces.

In one aspect of the present invention, intermediate portion 6 has a ribbed structure (RS), or a structure where any single member (rib) of that structure extends continuously from a location proximate the inner (or outer) portion to a location proximate the outer (or inner) portion. In another aspect of the invention, the RS is a structure where any rib connects at one end to a location proximate the at least one layer of the inner (or outer) portion and the other ends abuts or connects to another rib. Examples of RSs include corrugated materials, posts, curvilinear materials, honeycomb cores, and the like. These structures, as well as other RSs, are illustrated in FIG. 3.

A RS is advantageous because, for the additional weight added, the structural properties of the structural member are often substantially increased. The RSs contain both “ribs” and a large volume of voids. The “ribs” of the RS enhance the structural properties of the structural member while the voids are provided to minimize the weight of the RS. The respective amounts of ribs and voids present in the RSs used in the present invention depend on the configuration of the RS selected, e.g., which of those illustrated in FIG. 3 is selected. Preferably, the amount of voids should be maximized and the amount of ribs minimized, thereby giving the minimum weight for the maximum strength, provided the necessary (or desired) structural properties of the RS or the structural member is obtained.

The RSs employed in the present invention can be incorporated into the structural member in any suitable manner. In one aspect of the invention, the RS can be incorporated as a standalone “rib” extending from the at least one layer of the inner portion to the at least one layer of the outer portion, such as the configurations illustrated in FIG. 3. In another aspect of the invention, the rib can be connected to a supporting sheet(s) or another rib(s) where the sheet(s) or other rib(s) itself is connected to the at least one layer of the inner or outer portion.

If desired, additional materials can be incorporated into the ribbed structure. Examples of additional materials that can be incorporated into the RS include be filled with materials other than air, such as resins, foams, insulating materials, or NVH (noise, vibration, or harshness) damping materials, and/or the like.

The RS need not be uniform in the structural member. In one aspect of the embodiment, the type of ribs in the RS can vary from location to location. Further, multiples types of RSs can be combined in the at least one layer of the intermediate portion. In another aspect of the invention, the periodicity and/or thickness of the ribs can be changed in different areas of the at least one layer of the intermediate portion. In another aspect of the invention, the strength and other physical properties of the ribs can change from one location to another.

The ribs of the RS can be made of any suitable material exhibiting the desired structural properties. Suitable materials include any material known in the art to provide such a function, including materials having individual cells like beads, corrugated materials, thermoplastic molded materials, honeycomb materials, and foams such as flexible expanded plastic foams, polymer foams, metal components, flexible metal (i.e., aluminum) foams, or any combination of these materials. See, for example, U.S. Pat. Nos. 5,344,038, 4,573,707, 5,562,981, 4,128,963, 4,968,545, and 5,894,045, the disclosures of which are incorporated herein by reference.

A preferred intermediate portion 6 may be formed using honeycomb materials (also known as honeycomb cores). These materials usually comprise a thin sheet (or sheets) of material, such as paper or aluminum foil, which is formed into a variety of random or geometric cellular configurations. See U.S. Pat. No. 5,876,654, the disclosure of which is incorporated herein by reference. Honeycomb cores, which have a geometric cellular configuration, are known to have structural properties or characteristics that are superior to most foam or solid cores with a comparable density. Honeycomb cores can be made of various shapes and types of materials such as aluminum, aramid materials such as Korex®, nylon materials such as Nomex®, plastic, reinforced phenols, carbons, and fiberglass, or a combination thereof. Preferably, honeycombs made of Nomex® are employed as the material for intermediate portion 6.

The material and configuration (width, length, and geometric shape) of the cells can be optimized to provide the desired support and/or stabilization to the inner and outer portions. For example, the cell size can range from about ⅛ to about {fraction (3/4)} inches, and is preferably about {fraction (3/16)} inches.

The cells of the honeycomb cores can be filled with materials other than air, such as resins, foams, insulating materials, or NVH (noise, vibration, or harshness) damping materials, and/or the like. The type of material used, the thickness, the cell configuration, and “fill-in” material for intermediate portion 6 can vary along the length of structural member 2.

The configuration of inner portion 4, optional intermediate section 6, and outer portion 8 can vary within structural member 2. For example, the materials used for the composite, the fiber orientation, and the curvature, thickness, shape and other characteristics of the inner, intermediate, and/or outer portions can differ along the length and width of structural member 2. See, for example, U.S. Pat. No. 5,718,212, the disclosure of which is incorporated by reference.

The structural member of the invention may, if desired, have additional layers or portions on the outside of outer portion 8. In one example, a layer of metal, insulation, another composite material, or honeycomb core material may be placed over outer portion 8. Numerous additional portions or layers, including similar or different composite materials, could be added in a similar manner. In addition, at least one structural component, such as a bracket, coupler, cap, or the like, could be located on structural member 2.

The structural member of the present invention may have any substantially non-flat contour or configuration. FIG. 4 illustrates several such configurations. In one aspect of the invention, the structural members of the present invention can be configured with any contoured shape known in the art. The contoured shapes can have any combination of inner or outer shapes, inner and outer thickness, and inner or outer radii.

In one aspect of the invention, the structural members of the present invention have the contoured shapes illustrated in FIG. 16. The contoured shapes have a thickness and/or a radius that varies—either regularly or irregularly—along the length of the structural member. For example, referring to FIG. 16, the structural member 2 comprises a first portion 41 with a first diameter, a second portion 42 with a second diameter, and a third portion 43 with a third diameter. As another example, as illustrated in FIG. 17, the structural member 2 comprises a first portion 46 with a first thickness, a second portion 47 with a second thickness, and a third portion 48 with a third thickness.

In another aspect of the invention, the shape of the structural member has a shape other than substantially circular in cross-section. Examples of such shapes include rectangular, hexagonal, octagonal, polygonal, etc. . . . Making the tube with polygonal shape—such as a hexagon—provides several flat surfaces on the inner or outer surface of the structural member, which becomes important when bonding the surface of the structural member to another member, such as a metal end piece like the brackets mentioned above.

Creating a polygonal shape, however, creates a secondary loading condition on the structural member. This loading condition is usually localized near the bond surface and can easily be great enough to explode the structural member from the inside. To protect against such a problem, that area of the structural member 2 can be “overwrapped” with a composite collar comprising of fibers which are oriented around the circumference of the structural member. This prevents the structural member from exploding, while not adding much weight. The overwrap is located over the entire joint area with some extension past the joint to help with stress concentrations.

In another aspect of the invention, the shape of the structural member can be “shaped” or modified to be not substantially straight (or bent). In one aspect of the invention, the structural member (or a portion thereof) can made with a substantially non-straight shape. For example, as described in more detail below, the structural member of the invention could be made using a substantially non-straight mandrel to obtain the substantially non-straight shape as illustrated in FIG. 18. In another example, the structural member could be made by roll wrapping the inner, intermediate and outer portions on a hollow, flexible, straight shaped mandrel, and then bending to a desired shape and curing to obtain the shape illustrated in FIG. 18. The structural members of the invention can have a non-circular cross-section (triangular, rectangular, hexagonal, elliptical, and the like) as well as a substantially non-straight shape, as depicted in FIG. 19.

In another aspect of the invention, the structural member (or a portion thereof) can be made with a substantially straight shape, and then bent to have a substantially non-straight shape. For example, the structural member could be made by roll wrapping the inner, intermediate and outer portion on a hollow straight-shaped mandrel with a bladder, subjecting the assembly into a freeze, then removing the mandrel, and finally placing the intermediate structure in a mold and curing it in the mold. The structural member can be modified or bent using any number of methods as described in more detail below.

Additional structural components are added to modify the structural member for any desired end use. In one aspect of the invention, additional structural components are added to make it suitable as a part or component in any type of vehicle, whether motorized or not, and whether traveling on land, water, or in the air. For example, the structural member can be modified by adding those structural components necessary to have the structural member serve as a bumper, cross car beam, frame rails, etc. . . .

Structural member 2 can be made crushable by any manner in the art. In one aspect of the invention, the structural members are made crushable by including at least one crushing initiator (or initiator) adjacent to (or in) portion 4, portion 6, and/or portion 8. For example, as depicted in FIG. 12, the at least one initiator 14 can be incorporated in outer portion 8. However, the at least one initiator can be incorporated in inner portion 4, intermediate portion 6, and/or outer portion 8, as well as between these portions.

The initiator controls the location where, when an external load is applied, structural member 2 begins to deform. Often, the structural member resists impacts along its longitudinal axis. By including an initiator, the structural member of the present invention absorbs the energy of the load by undergoing a localized crush where the initiator is located, in modes such as transverse shearing, lamina bending, or local buckling like monocell buckling, face wrinkling, or core-shear instability. Thus, the initiator leads to a localized crush of the member so the structural member does not fail at other places. By incorporating at initiator, the preferred site of collapse of the structural member can be selected before the expected load is applied.

Any suitable initiator known in the art can be employed in the present invention, including those described in U.S. Pat. Nos. 4,742,889, 5,732,801, 5,895,699, and 5,914,163, the disclosures of which are incorporated herein by reference. The initiator can be placed at any location of structural member 2 depending on the desired characteristics including the crushing strength and crushing length. Preferably, the initiator is not located at the ends of structural member 2. More preferably, the initiator is placed at least about {fraction (1/2)} inch to about 2 inches away from any end of structural member 2.

Multiple initiators can be placed along separate portions of member 2 to deform (and therefore crush) several locations. Multiple initiators can also be placed proximate one another at a single portion of member 2 to deform that selected location. The number of initiators can vary, depending on the desired crushing strength and desired crushing length.

The initiator(s) can be of various shapes, sizes, and configurations, but should be substantially similar to the configuration of portion 4, intermediate portion 6, and/or portion 8. The width of the initiator can vary depending on the expected load, the desired crushing strength, and the desired crush length. For example, the width can range from about {fraction (1/16)} inches to about 1 inch, and is preferably about {fraction (1/2)} inches. The shape of the initiator can also vary depending on the expected load, the desired crushing strength, and the desired crush length. Generally, the shape is similar to that portion of structural member 2 into which it is incorporated. Thus, the shape can vary from circular, to rectangular or triangular, to any polygonal shape.

When multiple initiators are employed, they can be located in any desired location. In one aspect of the invention, the initiators can be either staggered or inline. The initiators can be inline, meaning that multiple initiators are aligned along the length or diameter of the structural member. The initiators can also be semi-staggered or fully staggered. In a semi-staggered position, the initiators are only partially aligned along a length or diameter of the structural member, e.g., they have overlapping positions (as illustrated in FIG. 13). In a fully staggered position, the initiators are not aligned along the length or diameter of the structural member, e.g., they have no overlapping positions (as illustrated in FIG. 14).

Any suitable material can be used for the initiator(s) of the present invention. Suitable materials used for the initiator can be any material which causes, as explained below, the respective inner and/or outer portion to deform and do not adhere to the materials used in the inner, intermediate, and/or outer portion. Examples of suitable materials include as teflons, rubber bands, brominated teflon coated glass fabric (brominated films), release films, rubber films, polytetrafluoroethylene (PTFE) tape, backing papers, or a combination thereof. In one aspect of the invention, brominated (“bromo”) films are preferably employed as the material for the initiator in the present invention.

Bromo films are brominated PTFE coated fiber glass fabric films. Bromo films are usually an impermeable layer that does not bond to the composite material during the curing process (as described below). There are two types of bromo films that can be employed as the initiator material: porous and non-porous. Preferably, a non-porous bromo film is employed as the initiator material, ensuring that there is an unbonded area in any desired location that will cause the failure in that particular location. Numerous bromo films are commercially available, including “Release Ease 234TFP” sold by Air Tech Advanced Materials Group.

It is believed that the initiator works because of the absence of a continuous layer in the inner, intermediate, and/or outer portion. Thus, the initiator could also be a gap or discontinuity (such as a stress riser) in the layer(s) of the inner, intermediate, and/or outer portion. The discontinuity could be a singular discontinuity such as a fold or irregularity, or plural discontinuities such as a row or column of cut-outs having any desired shape and size. For example, as illustrated in FIG. 15, a row of cut-outs can be located in a layer of the inner and/or outer portion, as well as the intermediate portion, so that when assembled, structural member 2 contains at least one initiator 14. In addition, when the impact load is an axial load, the initiator could be any material (or lack thereof) which operates as a local stress riser.

The present invention can be made by any suitable process yielding the structure of structural member 2. Suitable process for making the composite layer(s) include any processes known in the art, such as thermoforming, bladder or resin transfer molding, or inflatable mandrel processes, as described in U.S. Pat. Nos. 5,225,016, 5,192,384, 5,569,508, 4,365,952, 5,225,016, 5,624,519, 5,567,499, and 5,851,336, the disclosures of which are incorporated herein by reference. Another suitable process is a vacuum bagging process, such as described in U.S. Pat. No. 5,848,767, the disclosure of which is incorporated herein by reference. Other suitable processes are a filament winding process or sheet or tube rolling (also known as roll wrapping). See, for example, U.S. Pat. Nos. 5,632,940, 5,437,450, 4,365,952, 5,624,529, 5,755,558, 4,885,865, 5,332,606, 5,540,877, 5,840,347, and 5,914,163, the disclosures of which are incorporated herein by reference.

In the filament winding process, filaments of the desired material are dispersed in a matrix of binder material and wound about any suitable substrate, such as a mandrel assembly, with a shape generally corresponding to the desired shape (core region 10) of structural member 2. Any suitable mandrel, including those described in U.S. Pat. Nos. 5,795,524, 5,645,668, 5,192,384, 5,780,075, 5,632,940, 5,817,203, and 5,914,163, the disclosures of which are incorporated by reference, can be employed in the present invention. The substrate or mandrel must have sufficient strength, desired shape, and be able to withstand the processing conditions for making the structural member, e.g., ductile enough to be able to be manufactured (or bent after manufacture) to the desired shape. Suitable mandrels include those made of metals like steel and aluminum, polycarbonate, thermoset or thermoplastic rubber materials, thermoplastics (including flexible thermoplastics), or RRMM (including flexible RRMM) materials. The mandrels may be solid or hollow.

The filaments are wound over the mandrel and are reciprocally displaced relative to the mandrel along the longitudinal or winding axis of the mandrel to build portion 4. Additional portions, structures, or layers, such as additional metal or composite layers, can be added as described herein or as known in the art.

Preferably, the present invention employs a tube rolling (also known as roll wrapping) process for making the structural member of the present invention. One exemplary tube rolling process is illustrated in FIG. 5. The tube rolling process employs discrete sheet(s) of the metal-containing material or sheet(s) (or plies or laminates) of the desired composite material rather than filaments. The sheet(s) is interleaved, wrapped, or rolled over a mandrel assembly such as at least one mandrel 20. If desired, a release film can be applied to the mandrel prior to rolling any materials thereon. When more than one sheet is employed, the sheets can be stacked as illustrated in FIG. 2—prior to or during the rolling process—by hand or by any suitable mechanical apparatus, with the fibers of the composite material oriented in the desired orientation. When a continuous metal sheet is used, there is no need for such a stacking operation. After forming inner portion 4, the material comprising intermediate portion 6 is placed, preferably by wrapping or rolling, on inner portion 4 by hand or mechanical apparatus. The roll wrapping process is then resumed to apply the material of outer portion 8. Further details about roll wrapping processes are described in Engineered Materials Handbook, Volume 1: Composites, ASM International, pp. 569-574 (1987), the disclosure of which is incorporated herein by reference. Additional layers or materials-such as a coating-can be added over outer portion 8, if desired, in a similar manner or as known in the art.

The layers of the individual portions (inner, intermediate, and outer) can be cut and/or patterned such that when roll wrapped, the ends of individual sheet(s) substantially abut when rolled, thereby forming a butt joint 30. Preferably, the butt joint formed by the ends of any single sheet is staggered from the butt joint formed by the ends of an adjacent sheet, as illustrated in FIG. 6. Of course, when a continuous metal sheet is rolled, no butt joint occurs.

Inner portion 4 and outer portion 8 may be formed using different methods. For example, inner portion 4 can be formed by filament winding and outer portion 8 by roll wrapping, or vice versa. In this aspect of the invention, inner portion 4 may be fully cured prior to the application of intermediate portion 6. Similarly, inner portion 4 and intermediate portion 6 may be applied and cured together prior to the application of outer portion 8. Other methods known in the art, such as those described above, could also be combined with roll wrapping to make the structural members by performing discrete steps by different methods. For example, inner portion 4 could be formed using the filament winding process, intermediate portion 6 and outer portion 8 could be formed using the roll wrapping process, and then this intermediate structure could be constrained using a vacuum bagging process.

If desired, a bonding agent can be placed between successive layers of portions 4, 6, and/or 8. The bonding agent can be placed on selected areas only, or in a pattern such as in rows and/or columns, or over entire areas of the layer(s)/portion(s). Any suitable agent which helps bond the layers and is compatible with all of the processes employed to make structural member 2 can be employed, including glues, curing agents, adhesive materials, or a combination thereof. See, for example, U.S. Pat. No. 5,635,306, the disclosure of which is incorporated herein by reference. The bonding agent can be applied by hand or mechanical apparatus prior to, during, or after the assembly of the respective portion on the substrate.

Where portions 4, 6, and 8 are successively layed up in an uncured (e.g., B-stage state), the structure has outer portion 8 overlying intermediate portion 6, which overlies inner portion 4, which overlies the mandrel. If necessary to better bond and connect inner portion 4, intermediate portion 6, and outer portion 8 together, the intermediate structure formed by these portions can be constrained. The intermediate structure can be constrained by applying a suitable compressive force. This can be done using any suitable means including compressive dies or molds, vacuum bagging, or by using a suitable constraining means, e.g., by placing it in a plastic or metal mold, or by applying a suitable shrink-wrap tape(s) 22 or tube made of nylon, silicone, or polypropylene. During the curing process described below, the compressive means (e.g., the shrink-wrap tape or tube) applies suitable compressive force by physical or chemical change so that the materials of structural member 2 contact each other. When the RMM is used in the inner and/or outer portion of the present invention, the compressive force squeezes out excess resin during this curing process. See, for example, U.S. Pat. Nos. 5,600,912 and 5,698,055, the disclosures of which are incorporated herein by reference.

Moreover, if it is still necessary to better bond and connect the materials in the intermediate structure, they can undergo a suitable chemical reaction. For example, when inner portion 4 and/or outer portion 8 comprise a curable material (e.g., B-stage epoxy prepreg), the intermediate structure can be cured by any suitable means 24, such as an oven curing by applying heat and/or pressure or using an ultraviolet (u.v.) or microwave curing. The necessary heat and/or pressure depend on the size of the mandrel assembly and the materials used in structural member 2. During the curing process, the shrink-wrap tape or tube applies suitable compressive force. When the RMM is used in the inner and/or outer portion of the present invention, the compressive force squeezes out excess resin during this curing process.

The above process can be modified for structural members not having a substantially circular cross-section, including those with outer diameters having at least one flat area or area where the degree of curvature is substantially different from other surfaces of structural member 2. Examples of such structural members are illustrated in FIG. 4. As illustrated in FIG. 7, where the outer diameter has at least one relatively flat area, the shrink-wrap material (and accompanying compressive force) applied to the intermediate structure may not be uniform. Thus, bonding and connecting the materials to one another may not be uniform and, therefore, might impair the integrity of structural member 2. To more uniformly bond and connect such materials, at least one pressure distributor 26 is placed over the relatively flat areas of outer portion 8 prior to applying the shrink-wrap material. The pressure distributors “distribute” the applied compressive force more evenly to such flat areas, allowing a more uniform compressive force to all areas of the intermediate structure.

Any suitable shape of pressure distributors which evenly distribute the applied compressive force to the intermediate structure can be employed in the present invention. Exemplary shapes of the pressure distributors include substantially semicircular shapes (which provide a substantially circular outer surface) and T-shaped distributors where the flat end of the “T” abuts (and matches in size) the flat area of the intermediate structure and the long-end of the “T” extends outwards. Other shapes and configurations, including single components rather than plural components, could be employed provided they evenly distribute the compressive force over the flat area(s). For the structural member 2 like the one illustrated in FIG. 4, substantially semicircular pressure distributors 26 are depicted in FIG. 7. The pressure distributors of the present invention can be made of any suitable material that will maintain its shape when subjected to the compressive force, such as aluminum, steel, and silicone. Preferably, aluminum is employed as the material for the pressure distributor.

The shrink-wrap material can be placed under and/or over the pressure distributor(s). The shrink-wrap materials underlying the pressure distributors pressurize the corners, as well as keeping the pressure distributors from sticking to the intermediate structure. The shrink-wrap materials overlying the pressure distributors pressurize the flat areas.

The above process can be also be modified for structural members where the inner and outer portion do not have the same shape, such as those depicted in FIG. 11. Any suitable process modification which manufactures differently-shaped inner and outer portions can be employed in the present invention. The following two modifications to the above process demonstrate this concept. Other modifications could be envisioned, even though not demonstrated below.

First, the inner portion can have a substantially circular cross-section and the outer portion a non-circular cross-section. In such an instance, and as shown in FIG. 8, the process for making a circular-shaped structural member is followed as described above. To change the shape of the outer portion, a number of pressure distributors are placed over the circular-shaped outer portion prior to the constraining and curing stages. The number of pressure distributors used corresponds to the number of flat sides desired, e.g., four for a square, six for a hexagon, etc. . . . The process as noted above is then continued for the constraining and curing stages. During the constraining and curing process, the circular outer shape is changed to flat sides of the desired polygonal shape by the pressure exerted via the pressure distributors.

Second, the inner portion can have a substantially polygonal shape (i.e, square) and the outer portion a substantially circular shape. In this aspect of the invention as depicted in FIG. 9, the process for making a square-shaped structural member is followed as described above. To change the shape of the outer portion, the pressure distributors which are normally placed over the outer portion prior to the constraining and curing stages are omitted. Thus, the square-shaped outer portion is just wrapped with the constraining means. The process as noted above is then continued for the constraining and curing stages. During the constraining and curing process, the outer shape is changed to a substantially circular shape by the pressure exerted via the constraining means.

When used, the constraining means are then removed from the intermediate structure. For the plastic or metal mold, the mold is opened and removed. The shrink-wrap tape or tube may have reacted during the curing process to form a thin shell and, if desired, may be removed by hand or by a mechanical apparatus. When used, the pressure distributors are also removed.

In another aspect of the invention, the constraining means can be left on the outer portion either temporarily or permanently. For example, the shrink-wrap tape could be left on the structural member in the form as a thin shell for protection during shipping and then removed later. In another example, the shrink-wrap tape could be left on the structural member permanently as a protective coating.

Through the constraining and curing processes described above, the inner portion and the outer portion are chemically attached and/or or connected to the intermediate portion. Preferably, the materials of the inner and outer portion both chemically bond to the material of the intermediate portion, thus forming a substantially permanent physical bond.

Next, the substrate or mandrel may be removed from structural member 2 to form core region 10. The mandrel may be removed by any suitable process, including any known in the art which safely removes the mandrel without adversely impacting structural member 2, such as those disclosed in U.S. Pat. Nos. 5,900,194 and 5,306,371, the disclosures of which are incorporated herein by reference. If desired, core region 10 can be filled by any desired material as known in the art.

The mandrel can be either a removable mandrel or an integral mandrel. A removable mandrel is a mandrel that, as described above, is used in the roll wrapping process and then removed to create interior 10. An integral mandrel is a mandrel which becomes part of structural member 2 and is not removed. Thus, the mandrel remains in core region 10 and becomes a part of structural member 2.

When using an integral mandrel, the structural member 2 and the process for making that member are modified from the above description. In this aspect of the present invention, the intermediate portion is provided over the integral mandrel, and then the outer portion is provided over the intermediate portion. The structural member then follows the processing described above, with the exception that the integral mandrel is not removed. Thus, the integral mandrel can serve as the inner portion. If desired, an inner portion could still be included over the integral mandrel, yielding a structural member with an integral mandrel, an inner portion, an intermediate portion, and an outer portion.

At least one initiator 14 may be included in the present invention by any suitable method, including those known in the art. If only one layer is employed for portion 4, intermediate portion 6, and/or portion 8, the initiator can be created under, in, or over that single layer. When more than one layer is employed for such portions, such an initiator(s) can, additionally or alternatively, be included between the layers making up the respective portion.

For example, when the initiator is a gap or discontinuity in portion 4, intermediate portion 6, and/or portion 8, the desired section of that portion can be removed or altered. Any gap or discontinuity is preferably, although not necessarily, formed in the material prior to the roll wrapping operation. The initiator can consist of rows or columns of cutouts of any desired shape and size, as exemplified in FIG. 15, in the respective material which have been removed by any suitable process known in the art, such as stamping. The desired configuration for the initiator is selected, the desired location(s) for deformation of the structural member are determined, and the initiator(s) is then placed by creating a gap or discontinuity in the respective layer(s) of portion 4, portion 6, and/or portion 8 either before or after the rolling operation.

As another example, when the initiator is similar to that illustrated in FIG. 12, the desired width of the initiator material can placed on the selected locations(s) of portion 4, intermediate portion 6, and/or portion 8. The initiator material could be placed by rolling or wrapping the initiator material under or on the respective inner, intermediate, and/or outer portion. Alternatively, the initiator material could be placed in or on the sheet(s) prior to the rolling or wrapping process, e.g., by manufacturing the sheet(s) with the initiator formed therein. The desired material and configuration for the initiator is selected, the desired location(s) for deformation of the structural member are determined, and the initiator(s) is then placed under, over, or within the layer(s) of portion 4, 6, and/or 8 either before or after the rolling operation.

Once formed, the structural members of the present invention can be modified or cut for any desired use. For example, the structural members illustrated in FIGS. 5 and 7-9 have been cut in half along its length to provide two structural members. Likewise, the structural members could be cut along its length to provide any number of members with the desired length(s). Numerous shapes and configurations can be made by cutting along any dimension of the structural members, especially when combined with the broadest aspects of the processes of the present invention. A few examples of such shapes and configurations are shown in FIG. 10.

In one aspect of the invention, the structural members are manufactured with a substantially non-straight or bent shape as illustrated in FIGS. 18 and 19. In this aspect of the invention, a procedure similar to the process depicted in FIG. 20A is employed. When the inner, intermediate, and outer portions are formed on the mandrel, such portions (and the structural member) will have a similar shape. The structural member is then cured and molded. If necessary, non-solid mandrels 120 (such as inflatable or mandrels having separable parts) can be used (or substituted for a solid mandrel) in order to help remove the mandrel after the structural member has been made. See, for example, FIG. 20 illustrating that the mandrel can be removed before or after the molding stage.

In another aspect of the invention, the structural member (or a portion thereof) can be formed in an alternative manner. In this aspect of this invention, the curing and molding stages can be combined in a single step as illustrated in FIGS. 21 and 21A, where FIGS. 21 and 21A depict a different type of curing/molding procedure. Otherwise, the process is substantially the same as that described above.

In another aspect of the invention, the structural member (or a portion thereof) can be formed in an alternative manner. In this aspect of the invention, and as illustrated in FIG. 22, a part of the structural member (such as the inner portion) or a length-wise section of the structural member is made substantially straight and then is modified (bent) into a substantially non-straight shape. Thus, any number of bent shapes and complex configurations can be obtained for the inner portion. In this aspect of the invention, a hollow inner portion 4 is made using any of the methods known in the art, such as filament winding, roll wrapping, extrusion, molding, pultrusion, or braiding, and then it can be modified (or bent) into a non-straight shape using vacuum forming, thermoforming, hydroforming, bladder molding, etc. . . . The shape of the inner portion can be any desired shaped including triangular, rectangular, hexagon, polygon, elliptical, etc. . . .

Next, the resulting structure is heated and placed into a mold or a cast. In this step, an external mold with the desired shape—the inner shape of the mold is the same shape as the outer surface of the structural member) is fit over the outside of the intermediate structure (or vice versa). The external mold can be made of any material as known in the art that is capable of withstanding the operating pressures and temperatures used in the molding process, such as steel, aluminum, or a composite material.

After placed in the mold, the shape of the structural member is then modified to match the size of the mold. This step can be performed using any known forming technique known in the art, such as hydroforming, bladder molding, vacuum forming, or thermoforming. See, for example, U.S. Pat. Nos. 6,055,715, 6,183,013, and 6,216,509, the disclosures of which are incorporated herein by reference. In one aspect of the invention, an internal pressure (within inner portion 4) is applied in any suitable manner. In one aspect of the invention, the internal pressure is applied using a fluid such as a gas or liquid like as water. The inner surface of the inner portion 4 can be protected during this step using pressurized tubing or a barrier film on the inner surface of inner portion 4.

When applied correctly, this internal pressure modifies the shape of the structural member to conform to the mold. The time and amount of pressure is selected so that the structural properties (other than the shape) of the member are not damaged, as well as the desired dimensions are retained.

Next, optional intermediate portion and the outer portion are applied using any of the above-mentioned methods. When used, the materials used for the intermediate portion must be selected to permit bending—both stretching and contracting—of the intermediate portion. In this aspect of the invention, flexible foams, preformed honeycomb, or any preformable materials can be employed as the material for the intermediate portion. If a mandrel is used in this part of the process, the preformed intermediate portion can be cut open and then removed.

In yet another aspect of the invention, the inner and intermediate portion can be formed and then placed in the mold. After the shape of the inner and intermediate portions are modified as described immediately above, the outer portion is then formed on the intermediate portion, as depicted in FIG. 23.

Once the shape of the structural member has been modified, the mold is removed from the structural member. The member is then further processed as described above. In one aspect of the invention, additional structural components 130 such as brackets, fasteners, couplers, etc. can be added before structural member is cured that means they are in-mold.

In one aspect of the invention, such additional structural components could be attached to the structural members using any suitable technique. Suitable techniques include any known attachment technique, such as structural adhesive bonding, u.v. light cure adhesive bonding, film adhesive bonding, or other adhesive bonding technique. As well, new attachment techniques such as hot plate welding, ultrasonic, vibration, TP welding, injection molding, etc. could be used to attach the structural components.

As described above, any structural components known in the art—such as brackets, fasteners, couplers etc.—an be added to the structural member. In this aspect of the invention, the surfaces to be joined are cleaned with suitable solvent, followed by a surface abrasion for mechanical locking purposes. If desired, a suitable adhesive primer may be used. A suitable adhesive is then selected, weighed per the manufacturer's recommendation, mixed, and then applied on the surface to be joined. The parts are then assembled and held together with pressure using an appropriate fixture until the adhesive is substantially or fully cured.

Alternatively (or additionally), the structural members can be threaded on the inside and the parts can be threaded with a matching geometry. The parts and the structural member could then be threaded together, with the threads providing mechanical locking. In another aspect of the invention, the structural members are prepared with a hexagonal shape inside, and the parts are prepared with a matching hexagonal outer portion. The parts are then bonded to the structural member using an appropriate adhesive. The joined sections are then overwrapped with a “B” stage unidirectional material (such as a prepreg) in an oriented manner to provide additional torque resistance.

Generally, the method of bonding attachments depends on type of material (or substrate) to be bonded. If two similar materials—such as thermoplastic-based substrates—are to be bonded, other methods such as ultrasonic welding or hot plate welding can be utilized. If two substrates with dissimilar materials—such as metal to composite or to plastic—then a structural adhesive is utilized. As an example of this aspect of the invention, FIGS. 24 depicts a process for incorporating brackets in a composite-based bent structural member.

The structural member of the present invention has numerous uses such as a bumper, cross car beam, tie rod, torsion-bar, tube, beam, column, cylinder and the like and can be used in numerous industries. Primarily, the structural member can be used whenever a lightweight, strong, object is required. The structural member of the present invention can be used in the automotive, transportation, aerospace, and defense industries in applications such as airplane components, vehicle components such as tracks, trains, shipping containers, defense-related applications, recreational applications such as bikes, sail masts, shafts for golf clubs and racquets, or commercial applications such as bridges and buildings.

The following non-limiting examples illustrate the present invention.

EXAMPLE 1 (HYPOTHETICAL)

A cylindrical bent structural member with a circular cross-section can be made according to following process. A thin coat of a release material (Frekote 700NC or Axel EM606SL/SP) will be applied to a 3 inch diameter aluminum mandrel with a length of 52 inches.

Two metal (aluminum) sheets with preapplied adhesive and a thickness of about 0.001 inch will be pattern cut with a measurement of about 38 inches in width and about 48 inches in length. In both sheets, about 0.25 inch diameter holes, about 1 inch apart, will be punched about 2 inches away from the “side” end of the metal sheet. The holes will be punched, leaving the first 10 inches from the leading end of the sheet (that end first wrapped onto the mandrel) without any holes and the remaining 28 inches with holes.

One of the metal sheets will be then roll wrapped by hand onto the aluminum mandrel starting with the metal portion against the mandrel, e.g., so the adhesive material will be on the top. After rolling, the metal sheet of the inner portion will be four layers “thick” on the mandrel: the first layer containing those portions of the sheet with no punched holes and the least three layers having the punched holes.

Next, a honeycomb Hexcell Nomex® core with hexagonal shaped cells and a thickness of about 0.15 inches will be measured and cut to dimensions of about 10 inches by about 48 inches. About 0.25 inch diameter holes, about 1 inch apart, will be punched about 2 inches away from the “side” end of the honeycomb. This honeycomb core will be then roll wrapped by hand on the first metal sheet, with the honeycomb core adjacent to the adhesive of the last layer of the first metal sheet.

Next, the resulting intermediate structure will be placed in a freezer overnight. After cooling the structure, the mandrel will be removed and a bladder molding balloon will be introduced. The structure will be brought to room temperature and then placed in a bent mold. Pressure will be applied to the inside of the structure by inflating the balloon. The structure will then be subject to a curing process at about 250 degrees Fahrenheit for about 120 minutes during which the balloon will apply pressure to the intermediate structure from the inside and the mold will help to form the outer shape. After this curing process, the bladder will be deflated and the structural member will be removed from the mold.

EXAMPLE 2 (HYPOTHETICAL)

A cylindrical bent structural member with a square-shaped cross section can be made according to following process. A thin coat of a release material (Frekote 700NC or Axel EM606SL/SP) will be applied to a cylindrical aluminum mandrel with a 3.0 inch square outer diameter and a length of 72 inches. A bladder will be rolled over the mandrel.

One layer of Dacron/Teflon woven fabric will be cut about 11.6 inches in width and 64 inches in length. The individual sheet will be roll wrapped over the mandrel.

Four pairs of B-stage prepreg laminate sheets (8 individual sheets) containing anisotropic Kevlar fibers in an epoxy-based resin will be cut with measurements of about 11.6 to 13.4 inches in width and about 64 inches in length. The individual laminate sheets will then be overlaid so the fibers in successive sheets are symmetric and balanced at angles of ±15 degrees. The air between the stacked sheets will be removed by using a roller or other suitable device. Two pairs of the stacked prepreg sheets will be then roll wrapped by hand onto the aluminum mandrel.

Then, {fraction (1/2)} inch wide strips of bromo film will be measured and cut to a length similar to the outside diameter of the stacked sheets on the mandrel, e.g., 12½ inches in length. The strips will be then roll wrapped over the prepreg sheets on the mandrel. The strips will be located such, that when the structural member will be cut as described below, the strips will be about 2 inches away from any desired end of the structural member.

Next, a honeycomb Hexcell Nomex® core with hexagonal shaped cells and a thickness of about 0.2 inches will be measured and cut to dimensions of about 13 inches by about 64 inches. This honeycomb core will be then roll wrapped by hand on the first set of stacked prepreg sheets and strips of bromo film.

Additional {fraction (1/2)} inch wide strips of bromo film will be measured and cut to a length similar to the outside diameter of the honeycomb core. The strips will be then roll wrapped over the honeycomb core to be aligned with the strips under the core. The other two pairs of the stacked prepreg sheets will be then roll wrapped onto the honeycomb core and the strips of bromo film.

Next, the mandrel will be removed from the resulting intermediate by inflating bladder with a little air. The structure will then be placed in a bent mold with matching square shape mold. Pressure will be applied to the inside of the structure by inflating the bladder. The structure will then be subjected to a curing process at about 250 degrees Fahrenheit for about 120 minutes during which the bladder will apply pressure to the intermediate structure from the inside and the mold will help to form outer shape. After this curing process, the bladder will be deflated and the structural member will be removed from the mold.

EXAMPLE 3 (HYPOTHETICAL)

A cylindrical bent structural member with a circular cross-section will be made according to following process. A thin coat of a release material (Frekote 700NC or Axel EM606SL/SP) can be applied to a 0.729 inch diameter circular steel mandrel with a length of 64 inches.

A pair of B-stage prepreg laminate sheets (2 individual sheets) containing anisotropic carbon fibers in an epoxy-based resin can be cut with measurements of about 2.31 to 2.34 inches in width and about 60 inches in length. The individual laminate sheets can be overlaid so the fibers in successive sheets were symmetric and balanced at angles of ±80 degrees. The air between the stacked sheets will be removed by using a roller.

21 individual sheets of B-stage prepreg laminate sheets containing anisotropic carbon fibers in an epoxy-based resin will be cut with measurements of about 2.37 to 2.99 inches in width and about 60 inches in length. The individual laminate sheets will be overlaid so the fibers in successive sheets are symmetric and balanced at angles of ±10 degrees. The air between the stacked sheets will be removed by using a roller.

Another pair of B-stage prepreg laminate sheets (2 individual sheets) containing anisotropic carbon fibers in an epoxy-based resin can be cut with measurements of about 3.02 to 3.05 inches in width and about 60 inches in length. The individual laminate sheets will be overlaid so the fibers in successive sheets will be symmetric and balanced at angles of ±80 degrees. The air between the stacked sheets will be removed by using a roller.

Two layers of ±80, 21 layers of ±10, and another two layers of ±80 will be stacked and air between the stacked layers will be removed by using a roller. The stacked prepreg sheets will be then roll wrapped by hand onto the mandrel.

Next, the resulting intermediate structure can be shrink-wrapped. One layer of polyethylene-based shrink-wrap tape can be roll wrapped by a shrink-wrapping machine using gauge number 150 on the resulting structure. Next, the resulting intermediate structure will be placed in a freezer over night. After cooling the structure, the mandrel will be removed and a bladder introduced. The structure will be brought to room temperature and placed in a bent mold. Pressure will be applied to the inside of the structure by inflating the bladder. Alternatively, the structural member can be pressurized using hydroforming. The structure will then be subjected to a curing process at about 250 degrees Fahrenheit for about 120 minutes during which the bladder will apply pressure to the intermediate structure from the inside and the mold will help form the outer shape. After this curing process, the bladder will be deflated and the structural member removed from the mold.

Having described the preferred embodiments of the present invention, it is understood that the invention defined by the appended claims is not to be limited by particular details set forth in the above description, as many apparent variations thereof are possible without departing from the spirit or scope thereof. 

1. A shaped contoured structural member, comprising: an inner section containing a continuous plurality of contoured layers comprising both a layer of a composite material and a layer of a metal-containing material; an outer section containing a continuous plurality of contoured layers comprising both a layer of a composite material and a layer of a metal-containing material; and at least one intermediate layer having a honeycomb core structure connecting the inner section and the outer section.
 2. The structural member of claim 1, wherein the structural member has a substantially non-straight configuration.
 3. (canceled)
 4. (canceled)
 5. The structural member of claim 1, wherein the layers of metal-containing material are layers of metal alloy.
 6. The structural member of claim 1, further comprising at least one initiator. 